For operating aircraft as passenger airplanes it is very useful and, for automatic steering, necessary to provide information about forces and moments acting upon the aircraft specifically when starting and landing.
The U.S. Pat. No. 2,443,045 discloses a system determining the centre of gravity and the gross weight of an airplane on the ground prior to take-off. For this purpose a nose wheel strut has secured the two strain gauges on that portion of the strut bearing the direct load of the airplane. Main landing gear struts have strain gauges mounted in a similar manner. The airplane gross weight is equal to the sum of the loads supported by the main gear struts and the nose gear strut.
The U.S. Pat. No. 3,900,828 discloses an on-board tire strut fault apparatus for aircraft again using strain gauges for sensing the loading conditions on the ground. Defective degradations and faults of tire and/or strut suspensions are signalled automatically by way of electrical comparison of the output signals from diagonally disposed strain gauges. Again the weight and centre-of-gravity may be determined.
The German Laid Open Publication No. 36 20 888 relates to a system for monitoring the loading of structure components of aircraft using the capturing, processing and storing of load relevant parameters during the operation of the aircraft for evaluation on the ground for continuously monitoring a predetermined stability thereof. For this purpose output signals of sensors are processed and are provided for determining the speed acceleration mass centre of gravity and excursions of the wing lids.
The European Patent Application Publication No. 0066923 (U.S. Patent Application Ser. Nos. 265031 of May 18, 1981 and 371321 of Apr. 26, 1982) discloses an aircraft structural integrity assessment system similar to that discussed above but employing structural moment detectors to measure and record certain effects of forces acting on the structure of an aircraft.
The German Patent Laid Open Publication No. 30 43 055 (U.S. Patent Application Ser. No. 102776 filed on Dec. 12, 1979) discloses a mass measuring system for an aircraft using a pair of inclination sensors determining the bending angle of a part of the aircraft due to the gross weight thereof.
The U.S. Pat. No. 5,123,937 discloses a method for determining inclination changes of a wheel axle of a truck dependent on the load.
The U.S. Patent Application Ser. No. 057,892 filed May 21, 1987 (International Patent Application WO 87/02129) relates to a method and a system for operating ground vehicles using force/moment measuring devices integrated into elastic connections and/or support positions thereof, determining the forces and/or moments acting upon the vehicle or parts thereof by means of the force/moment measuring devices, processing these values and optimizing the operating characteristics of the vehicle on the basis of the results of the processing.
Aircraft are not mentioned in this publication though the one or other measurement indicated there may be applied for aircraft, too. However, in many aspects, the situation is much different for aircraft as compared with ground vehicles since quite different parameters have to be considered.
Essential aspects with aircraft are in particular the safety during starting and landing as well as a minimum of energy consumption. The safety during starting depends in particular on the rolling distance already covered, the actual momentary speed, the gross weight, the momentary boyancy, the position of the static and the aerodynamic centres of gravity and various other parameters. Energy consumption is essentially determined by the position of the aerodynamic centre of gravity in respect of the static centre of gravity. For landing to a major part similar aspects are applicable as for starting.